A multimeter, as the name suggests, is an instrument which is capable of measuring a number of different parameters, such as voltage, current, resistance, and the frequency of an input signal. Modern multimeters have become quite advanced and are also sometimes capable of measuring capacitance, duty factor, and temperature. It is also common for multimeters to automatically select the proper range for display.
Unfortunately, the user interface on the front panels of these existing multifunction multimeters is becoming more and more cluttered, confusing, and difficult to use. One reason for this clutter is the number of buttons (i.e., keys) and input terminals required to select and exercise the available features. For example, it is common for selector knobs to have three positions for the AMPS function (i.e., A, mA, and .mu.A), and at least two positions for the Volts function (AC and DC). There are usually two AMPs input connectors (i.e., AMPs and mA) in addition to the VOLTs and COMMON input connectors. Thus, the user is presented with a confusing multitude of legends, buttons and knobs, and inputs, from which he must choose to exercise the desired function.
It is known to use so-called "softkeys", to reduce the number of buttons needed, by changing the legend on a display screen adjacent to the button. The display device has to be versatile enough to display a number of different softkey legends. Such systems typically employ a CRT or a dot matrix LCD so that the area immediately adjacent to the button can be erased and a new legend displayed when the key function is to be changed. Unfortunately, in a handheld device such as a multimeter, a CRT is impractical for reasons of weight, size, and durability, and a dot matrix LCD is impractical for the added complexity and expense that its use would entail. What is needed is a user interface for a multimeter which retains the multifunction capability but overcomes the above noted difficulties.